My 2012 Colorado requires full throttle start after adding gas to the gas tank.

What is your question?

When I add gas to the gas tank I have to give the truck full throttle while turning the key to make the truck start. Then it requires hold the rpm's at around 1500-2000 rpm's for around 20 seconds roll the engine smoothes out & idles on its own.

What makes this problem better or worse?

Nothing seems to make it better or worse.

How long has your 2012 Chevrolet Colorado had this problem?

Around 2 years.